<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width= , initial-scale=1.0">
  <title>Document</title>
</head>
<body>
  <div id="container">
    <p id="text">当前数值为：100</p>
    <button id="btn1">点击增大</button>
    <button id="btn2">点击减小</button>
  </div>

  <script src="lib/jquery.js"></script>
  <script>
    var $text = $('#text');
    var $btn1 = $('#btn1');
    var $btn2 = $('#btn2');

    var num = 100;

    $btn1.on('click', function () {
      num++;
      $text.text('当前数值为：' + num);
    });

    $btn2.on('click', function () {
      num--;
      $text.text('当前数值为：' + num);
    });
  </script>
</body>
</html>